1. Field of the Invention
This invention relates to a process of taking liquid from large-volume, deep vessels by means of sucking vessels having sucking elements which are short relative to the depth of the deep vessels, wherein liquid is sucked from a liquid volume which is contained in said deep vessel and has a changing depth.
This invention relates also to an auxiliary sucking device for use with large-volume, deep vessels in carrying out the process, comprising a tube, which is adapted to be introduced into the deep vessel, and a check valve, which is associated with the flow area of the tube and prevents a downward flow in the tube, and a bowl, which is detachably mounted on the deep vessel and contains a mouth adjacent to the top end of the tube that is provided with the check valve.
2. Description of the Prior Art
German Patent Specification No. 29 26 691 discloses a repeat pipette, which is to be connected to a syringelike vessel, which comprises a cylinder body and at one end a conical tip.
A piston is reciprocable in the cylinder body so that liquid can be sucked in that the piston is retracted and can be discharged in that the piston is advanced. To reduce the air volume the piston is suitably provided with a conical extension, which protrudes into the conical tip. The conical tip has a predetermined length and a predetermined external shape. In laboratory work, the vessel is connected to a repeat pipette and used to suck liquid and to discharge metered liquid.
Whereas such syringelike sucking vessels can be used for various purposes, problems will arise when liquids are to be taken from a deep vessel, such as a relatively large bottle, because the syringe will reach the liquid in the bottle when the latter is full but will no longer dip into the liquid when a substantial amount of liquid has been taken.
From German Patent Specification No. 32 04 178 it is known to provide a pipetting device with a mechanism for retaining a detachably inserted syringe and with means for a convenient discharge of small metered amounts of liquid. But that known syringe also has only a relatively short discharge tip, which gives rise to the problems outlined hereinbefore.
For this reason the use of the repeat pipette and the pipetting device will give rise to problems when liquids are to be taken from supply vessels in laboratories.
The liquids to be taken may consist of organic and inorganic liquids, solvents, acids, alkalies and reagents, and may have to be handled in milliliter amounts.
That reference to amounts is not made in a restricting sense because amounts of different orders of magnitude may be handled if the dimensions are properly selected.
EPA No. 0 212 964 discloses a sampling tube, which is provided with a check valve and is adapted to be introduced into a vessel so that liquid can be taken when a suction force is applied to the top end of the tube. A valve fitting may be detachably fitted on the tube at its top end to communicate through a constricted passage with the interior of the tube and in a chamber formed with through openings contains a small valve member. But that valve member is not required to effect an absolutely tight seal because a liquid level is desired to be maintained in the tube by the surface tension of the liquids. For this reason the sampling tube can be used only to handle certain liquids.
That known device has the purpose to provide a simple device in which the valve which is fitted on the tube can be discarded after a single use whereas the tube, which in that device constitutes a separate part, can be washed out and re-used. That tube consists of glass and for that reason cannot readily be cut to length. Besides, that tube is used only to take a sample by the exertion of a suction force so that syringelike suction vessels cannot be used because there is an undefined empty space above the valve.
In view of the above remarks it may be desired in laboratories to suck equal amounts of liquid from supplies in which the liquid level changes as liquid is taken. So-called bottle dispensers are known, which constitute inserts of substantial size and are operated by pump systems and discharge into an open receiving vessel from which liquid can then be taken. In that case liquid is indirectly taken from a vessel and the transfer into the receiving vessel will involve a considerable occlusion of air and evaporation. The operation is complicated and the known dispensers are very expensive.
Other known devices comprises a handling or receiving vessel which can be compressed to directly discharge or to receive in a supply space a liquid in an amount which can hardly be accurately defined. The capacity of such receiving space may arbitrarily be changed by an additonal control device. This will not permit a taking of an accurate amount of liquid as is contemplated in connection with the present invention. For the purposes of the invention it is contemplated that syringelike sucking vessels known as pipettes will always be used.